Method of forming an inductor on a semiconductor wafer

ABSTRACT

A semiconductor device has a substrate with an inductor formed on its surface. First and second contact pads are formed on the substrate. A passivation layer is formed over the substrate and first and second contact pads. An insulating layer is formed over the passivation layer. The insulating layer is removed over the first contact pad, but not from the second contact pad. A metal layer is formed over the first contact pad. The metal layer is coiled on the surface of the substrate to produce inductive properties. The formation of the metal layer involves use of a wet etchant. The second contact pad is protected from the wet etchant by the insulating layer. The insulating layer is removed from the second contact pad after forming the metal layer over the first contact pad. An external connection is formed on the second contact pad.

FIELD OF THE INVENTION

The present invention relates in general to semiconductor devices and,more particularly, to formation of an inductor on a semiconductor wafer.

BACKGROUND OF THE INVENTION

Semiconductor devices are found in many products used in modern society.Semiconductors find applications in consumer items such asentertainment, communications, networks, computers, and household itemsmarkets. In the industrial or commercial market, semiconductors arefound in military, aviation, automotive, industrial controllers, andoffice equipment.

The manufacture of semiconductor devices involves formation of a waferhaving a plurality of die. Each die contains hundreds or thousands oftransistors and other active and passive devices performing a variety ofelectrical functions. For a given wafer, each die from the wafertypically performs the same electrical function. Front-end manufacturinggenerally refers to formation of the semiconductor devices on the wafer.The finished wafer has an active side containing the transistors andother active and passive components. Back-end manufacturing refers tocutting or singulating the finished wafer into the individual die andthen packaging the die for structural support and/or environmentalisolation.

One goal of semiconductor manufacturing is to produce a package suitablefor faster, reliable, smaller, and higher-density integrated circuits(IC) at lower cost. Flip chip packages or wafer level packages (WLP) areideally suited for ICs demanding high speed, high density, and greaterpin count. Flip chip style packaging involves mounting the active sideof the die facedown toward a chip carrier substrate or printed circuitboard (PCB). The electrical and mechanical interconnect between theactive devices on the die and conduction tracks on the carrier substrateis achieved through a solder bump structure comprising a large number ofconductive solder bumps or balls. The solder bumps are formed by areflow process applied to solder material deposited on contact pads,which are disposed on the semiconductor substrate. The solder bumps arethen soldered to the carrier substrate. The flip chip semiconductorpackage provides a short electrical conduction path from the activedevices on the die to the carrier substrate in order to reduce signalpropagation, lower capacitance, and achieve overall better circuitperformance.

In many applications, it is desirable to form passive circuit elements,including an inductor, on the semiconductor wafer. The inductor allowsthe IC to perform reactive circuit functions without using externalcircuit components. The inductors are formed as coiled or wound metallayers on the surface of the substrate. The deposition and patterning ofthe inductor metal layers typically involves a wet etching process. Thewet etchant can cause chemical degradation to other metal layers on thewafer surface, for example to external wire bond, solder bump, and RDLpads. The chemical degradation may cause defects in the externalconnection pad and reduce manufacturing yield.

A need exists to form an inductor without degrading other metal layerson the semiconductor wafer.

SUMMARY OF THE INVENTION

In one embodiment, the present invention is a method of making asemiconductor device comprising the steps of providing a substrate,forming first and second contact pads on the substrate, forming a firstpassivation layer over the substrate and first and second contact pads,forming an insulating layer over the first passivation layer, removingthe insulating layer over the first contact pad while maintaining theinsulating layer over the second contact pad, and forming a metal layerover the first contact pad. The metal layer is coiled on the surface ofthe substrate to produce inductive properties. The step of forming themetal layer involves use of a wet etchant. The second contact pad isprotected from the wet etchant by the insulating layer. The methodfurther includes the steps of removing the insulating layer from thesecond contact pad after forming the metal layer over the first contactpad, and forming an external connection to the second contact pad.

In another embodiment, the present invention is a method of making asemiconductor device comprising the steps of providing a substrate,forming first and second contact pads on the substrate, forming a firstpassivation layer over the substrate and first and second contact pads,forming an insulating layer over the first passivation layer, removingthe insulating layer over the first contact pad while maintaining theinsulating layer over the second contact pad, and forming a metal layerover the first contact pad. The metal layer is coiled on the surface ofthe substrate to produce inductive properties. The method furtherincludes the steps of removing the insulating layer from the secondcontact pad after forming the metal layer over the first contact pad,and forming an external connection to the second contact pad.

In another embodiment, the present invention is a method of making asemiconductor device comprising the steps of providing a substrate,forming first and second contact pads on the substrate, forming aninsulating layer over the first and second contact pads, removing theinsulating layer over the first contact pad while maintaining theinsulating layer over the second contact pad, forming a metal layer overthe first contact pad, the metal layer having inductive properties, andremoving the insulating layer from the second contact pad after formingthe metal layer over the first contact pad.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flip chip semiconductor device with solder bumps providingelectrical interconnect between an active area of the die and a chipcarrier substrate;

FIGS. 2 a-2 f illustrate a process of forming an inductor on asemiconductor wafer connected to a wire bond; and

FIG. 3 illustrates an alternate embodiment of the inductor formed on asemiconductor wafer and connected to a solder bump.

DETAILED DESCRIPTION OF THE DRAWINGS

The present invention is described in one or more embodiments in thefollowing description with reference to the Figures, in which likenumerals represent the same or similar elements. While the invention isdescribed in terms of the best mode for achieving the invention'sobjectives, it will be appreciated by those skilled in the art that itis intended to cover alternatives, modifications, and equivalents as maybe included within the spirit and scope of the invention as defined bythe appended claims and their equivalents as supported by the followingdisclosure and drawings.

The manufacture of semiconductor devices involves formation of a waferhaving a plurality of die. Each die contains hundreds or thousands oftransistors and other active and passive devices performing one or moreelectrical functions. For a given wafer, each die from the wafertypically performs the same electrical function. Front-end manufacturinggenerally refers to formation of the semiconductor devices on the wafer.The finished wafer has an active side containing the transistors andother active and passive components. Back-end manufacturing refers tocutting or singulating the finished wafer into the individual die andthen packaging the die for structural support and/or environmentalisolation.

A semiconductor wafer generally includes an active front side surfacehaving semiconductor devices disposed thereon, and a backside surfaceformed with bulk semiconductor material, e.g., silicon. The active frontside surface contains a plurality of semiconductor die. The activesurface is formed by a variety of semiconductor processes, includinglayering, patterning, doping, and heat treatment. In the layeringprocess, semiconductor materials are grown or deposited on the substrateby techniques involving thermal oxidation, nitridation, chemical vapordeposition, evaporation, and sputtering. Photolithography involves themasking of areas of the surface and etching away undesired material toform specific structures. The doping process injects concentrations ofdopant material by thermal diffusion or ion implantation.

Flip chip semiconductor packages and wafer level packages (WLP) arecommonly used with integrated circuits (ICs) demanding high speed, highdensity, and greater pin count. Flip chip style semiconductor device 10involves mounting an active area 12 of die 14 facedown toward a chipcarrier substrate or printed circuit board (PCB) 16, as shown in FIG. 1.Active area 12 contains active and passive devices, conductive layers,and dielectric layers according to the electrical design of the die. Theelectrical and mechanical interconnect is achieved through a solder bumpstructure 20 comprising a large number of individual conductive solderbumps or balls 22. The solder bumps are formed on bump pads 24, whichare disposed on active area 12. The bump pads 24 connect to the activecircuits by conduction tracks in active area 12. The solder bumps 22 areelectrically and mechanically connected to contact pads 26 on carriersubstrate 16 by a solder reflow process. The flip chip semiconductordevice provides a short electrical conduction path from the activedevices on die 14 to conduction tracks on carrier substrate 16 in orderto reduce signal propagation, lower capacitance, and achieve overallbetter circuit performance.

FIGS. 2 a-2 f illustrate formation of an inductor on a semiconductorwafer. FIG. 2 a illustrates a cross-sectional view of semiconductorwafer 28. Substrate 30 is made of silicon or other bulk semiconductormaterial. Substrate 30 is the foundation of the active IC wafer andincludes final metal and passivation. Contact pads 32 and 34 are part ofthe final metal and are patterned and deposited on substrate 30. Contactpads 32 and 34 can be made with aluminum (Al), copper (Cu), tin (Sn),nickel (Ni), gold (Au), silver (Ag), or other electrically conductivematerial. The deposition of contact pads 32 and 34 uses an evaporation,electrolytic plating, electroless plating, or screen printing process.Contact pad 32 will be used for the inductor connection. Contact pad 34,which may be electrically common with contact pad 32 will be used for anexternal wire bond connection, and additional input and output (I/O)redistribution connection.

A passivation layer 36 is a final passivation layer on semiconductorwafer 28 and is formed and patterned over the entire wafer, includingsubstrate 30 and contact pads 32 and 34. Passivation layer 36 can bemade with silicon nitride (SixNy), silicon dioxide (SiO2), siliconoxynitride (SiON), polyimide (PI), benzocyclobutene (BCB),polybenzoxazole (PBO), or other polymer material. A portion ofpassivation layer 36 is removed using a mask-defined photoresist etchingprocess to expose contact pads 32 and 34.

In FIG. 2 b, a thin insulating protective layer 38 is deposited bychemical vapor deposition (CVD) or physical vapor deposition (PVD) suchas sputtering, and then patterned over passivation layer 36 and contactpads 32 and 34. The insulating layer 38 follows the contour ofpassivation layer 36 and contact pads 32 and 34. The insulating layer 38can be made with SixNy, SiO2, SiON, tantalum pentoxide (Ta2O5), zincoxide (ZnO), or other material having dielectric properties. Thethickness of insulating layer 38 typically ranges from 250 to 3000angstroms (Å). In one embodiment, insulating layer 38 is 300-400 Å.

A portion of insulating layer 38 over contact pad 32 is etched using amask-defined etching process to expose contact pad 32. The opening ofinsulation layer 38 over pad 32 can be larger or less than the size ofcontact pad 32. Due to over-etching and selectivity, a portion ofpassivation layer 36 may also removed during the etching process, asseen by the notch or step in insulating layer 38 over contact pad 32.

At this stage, only contact pad 32 is exposed. Contact pad 34 remainscovered by insulating layer 38. The insulating layer 38 over contact pad34 protects the contact pad during the wet etching used to form adhesionlayer 40 and inductor layer 42, as described in FIG. 2 c, and preventsthe wet etchant from chemically degrading the metal in contact pad 34.Consequently, the thickness of contact pad 34 remains the same, in areasunder passivation layer 36 and in areas not under passivation layer 36,during the formation of inductor layer 42.

In FIG. 2 c, a metal adhesion layer 40 is deposited over and follows thecontour of contact pad 32 and the notched portion of passivation layer36. The adhesion layer 40 can be made with titanium (Ti), titaniumtungsten (TiW), or chromium (Cr). The thickness of adhesion layer 40ranges from 200-2000 Å, with a typical thickness of 1000 Å. A metallayer 42 is deposited and adhesive layer 40 is patterned using a wetetch process. The metal layer 42 is the inductor on semiconductor wafer28. The metal layer 42 and adhesion layer 40 are typically wound orcoiled in plan view on the surface of substrate 30 to produce or exhibitthe desired inductive properties, as shown by the three regions 40 inthe cross-sectional view of FIG. 2 c. The inductor layer 42 can be madewith Cu or Al. The deposition of inductor layer 42 uses an evaporation,electrolytic plating, electroless plating, or screen printing process.

In FIG. 2 d, a passivation layer 44 is formed over insulating layer 38and inductor layer 42 for structural support and physical isolation.Passivation layer 44 can be made with SiN, SiO2, SiON, PI, BCB, PBO, orother polymer material.

In FIG. 2 e, the portion of insulating layer 38 over contact pad 34 isremoved using a mask-defined plasma or dry etching process to avoiddamaging the contact pad metal. Wire bond 46 with bond wire 48 is formedon contact pad 34 for external electrical connection. In one embodiment,wire bond 46 connects to inductor layer 42, and potentially other thecircuit elements, by way of contact pads 32 and 34.

In another embodiment, a via is formed in passivation layer 44 using amask-defined plasma or dry etching process, as shown in FIG. 2 f. Thevia in the passivation layer 44 can be used as the mask for the plasmaor dry etch to remove the portion of insulating layer 38 over contactpad 34.

An alternate embodiment of the formation of an inductor on asemiconductor wafer is shown in FIG. 3. In the same manner described inFIGS. 2 a-2 f, contact pads 32 and 34 are patterned and deposited onsubstrate 30. Contact pad 34, which is electrically common with contactpad 32, will be used for an external connection. A passivation layer 36is formed over substrate 30 and contact pads 32 and 34. A thininsulating protective layer 38 is deposited and patterned overpassivation layer 36 and contact pads 32 and 34.

A portion of insulating layer 38 is removed using a mask-defined etchingprocess to expose contact pad 32. At this stage, only contact pad 32 isexposed. Contact pad 34 remains covered by insulating layer 38. Theinsulating layer 38 over contact pad 34 protects the contact pad duringthe wet etching used to form adhesion layer 40 and inductor layer 42, asdescribed in FIG. 2 c, and prevents the wet etchant from chemicallydegrading the metal in contact pad 34. Consequently, the thickness ofcontact pad 34 remains the same, in areas under passivation layer 36 andin areas not under passivation layer 36, during the formation ofinductor layer 42.

A metal adhesion layer 40 is deposited over and follows the contour ofcontact pad 32 and the notched portion of passivation layer 36. A metallayer 42 is deposited and patterned over adhesion layer 40 using a wetetch process. The metal layer 42 is the inductor on semiconductor wafer28. The metal layer 40 is typically wound or coiled in plan view on thesurface of substrate 30 to produce the desired inductive properties, asshown by the three regions 40 in the cross-sectional view of FIG. 2 c. Apassivation layer 44 is formed over insulating layer 38 and inductorlayer 42 for structural support and physical isolation.

The portion of insulating layer 38 over contact pad 34 is removed usinga mask-defined plasma or dry etching process to avoid damaging thecontact pad metal. In another embodiment, a via is formed in passivationlayer 44 using a mask-defined plasma or dry etching process, as shown inFIG. 2 f. The via in the passivation layer 44 can be used as the maskfor the plasma or dry etch to remove the portion of insulating layer 38over contact pad 34.

A redistribution layer (RDL) 50 is deposited over passivation layer 44and contact pad 34. RDL 50 can be made with Al, Ni, nickel vanadium(NiV), Cu, or Cu alloy. RDL 50 can be made with a single layer, ormultiple layers using an adhesion layer of Ti, TiW, or Cr. A passivationlayer 52 is formed over passivation layer 44 and RDL 50. Passivationlayer 52 can be made with SixNy, SiO2, SiON, PI, BCB, PBO, or otherpolymer material. A portion of passivation layer 54 is removed using amask-defined etching process to expose RDL 50. A metal layer 54 isdeposited over passivation layer 52 and RDL 50 by an evaporation,electrolytic plating, electroless plating, or screen printing process.Metal layer 54 is an under bump metallization (UBM) layer. UBM 54 can bemade with Ti, Ni, NiV, Cu, or Cu alloy.

An electrically conductive solder material is deposited over UBM 54through an evaporation, electrolytic plating, electroless plating, orscreen printing process. The electrically conductive material is anymetal, e.g., Sn, lead (Pb), Ni, Au, Ag, Cu, bismuthinite (Bi), andalloys thereof, or mixtures of other conductive materials. In oneembodiment, the solder material is 63 percent weight of Sn and 37percent weight of Pb. The solder material is reflowed by heating theconductive material above its melting point to form spherical ball orbump 56. In one embodiment, solder bump 56 is about 75 μm in height. Insome applications, solder bump 56 is reflowed a second time to improveelectrical contact to UBM 54. RDL 50 operates as an intermediateconductive layer to route electrical signals from inductor layer 42 tosolder bump 56.

While one or more embodiments of the present invention have beenillustrated in detail, the skilled artisan will appreciate thatmodifications and adaptations to those embodiments may be made withoutdeparting from the scope of the present invention as set forth in thefollowing claims.

1. A method of making a semiconductor device, comprising: providing asubstrate; forming first and second contact pads on the substrate;forming a first passivation layer over the substrate and first andsecond contact pads; removing a portion of the first passivation layerover the first and second contact pads; forming a protective insulatinglayer on a surface of the first passivation layer and first and secondcontact pads such that a top surface of the protective insulating layerfollows a contour of the first and second contact pads and surface ofthe first passivation layer, the protective insulating layer having athickness of 300-400 angstroms; removing the protective insulating layerover the first contact pad and surface of the first passivation layerwhile maintaining the protective insulating layer over the secondcontact pad; forming a metal layer on the first contact pad and surfaceof the first passivation layer, the metal layer also being formed on thetop surface of the protective insulating layer which follows the contourof the first and second contact pads and surface of the firstpassivation layer, the metal layer being coiled over the surface of thesubstrate to produce inductive properties, wherein forming the metallayer involves use of a wet etchant, the second contact pad beingprotected from the wet etchant by the protective insulating layer;forming a second passivation layer over the metal layer and protectiveinsulating layer; removing the protective insulating layer from thesecond contact pad after forming the second passivation layer; andforming an external connection to the second contact pad.
 2. The methodof claim 1, further including forming a wire bond on the second contactpad.
 3. The method of claim 1, further including: forming an under bumpmetallization layer in electrical connection to the second contact pad;and forming a solder bump on the under bump metallization layer.
 4. Themethod of claim 3, further including disposing a redistribution layerbetween the second contact pad and under bump metallization layer. 5.The method of claim 1, further including using the second passivationlayer as a mask to remove the protective insulating layer over thesecond contact pad.
 6. The method of claim 1, further including formingan adhesion layer between the first contact pad and metal layer.
 7. Amethod of making a semiconductor device, comprising: providing asubstrate; forming first and second contact pads on the substrate;forming a first passivation layer over the substrate and first andsecond contact pads; removing a portion of the first passivation layerover the first and second contact pads; forming an insulating layer on asurface of the first passivation layer and first and second contact padssuch that a top surface of the insulating layer follows a contour of thefirst and second contact pads and surface of the first passivationlayer; removing the insulating layer over the first contact pad andsurface of the first passivation layer while maintaining the insulatinglayer over the second contact pad; forming a metal layer on the firstcontact pad and surface of the first passivation layer, the metal layeralso being formed on the top surface of the insulating layer whichfollows the contour of the first and second contact pads and surface ofthe first passivation layer, the metal layer being coiled over thesurface of the substrate to produce inductive properties; forming asecond passivation layer over the metal layer and insulating layer;removing the insulating layer from the second contact pad after formingthe second passivation layer; and forming an external connection to thesecond contact pad.
 8. The method of claim 7, further including forminga wire bond on the second contact pad.
 9. The method of claim 7, furtherincluding: forming an under bump metallization layer in electricalconnection to the second contact pad; and forming a solder bump on theunder bump metallization layer.
 10. The method of claim 9, furtherincluding disposing a redistribution layer between the second contactpad and under bump metallization layer.
 11. The method of claim 7,further including forming an adhesion layer between the first contactpad and metal layer.
 12. The method of claim 7, wherein the insulatinglayer includes a dielectric material.
 13. The method of claim 7, furtherincluding using the second passivation layer as a mask to remove theinsulating layer over the second contact pad.
 14. A method of making asemiconductor device, comprising: providing a substrate; forming firstand second contact pads on the substrate; forming a first passivationlayer over the substrate and first and second contact pads; removing aportion of the first passivation layer over the first and second contactpads; forming an insulating layer on the first passivation layer andfirst and second contact pads such that a top surface of the insulatinglayer follows a contour of the first and second contact pads and surfaceof the first passivation layer; removing the insulating layer over thefirst contact pad while maintaining the insulating layer over the secondcontact pad; forming a metal layer on the first contact pad and topsurface of the insulating layer which follows the contour of the firstand second contact pads and surface of the first passivation layer, themetal layer having inductive properties; and forming a secondpassivation layer over the metal layer and insulating layer; removingthe insulating layer from the second contact pad after forming secondpassivation layer; and forming an external connection to the secondcontact pad.
 15. The method of claim 14, further including forming anexternal connection to the second contact pad.
 16. The method of claim14, further including forming a wire bond on the second contact pad. 17.The method of claim 14, further including: forming an under bumpmetallization layer in electrical connection to the second contact pad;and forming a solder bump on the under bump metallization layer.
 18. Themethod of claim 17, further including disposing a redistribution layerbetween the second contact pad and under bump metallization layer. 19.The method of claim 14, further including forming an adhesion layerbetween the first contact pad and metal layer.
 20. The method of claim14, wherein the insulating layer includes a dielectric material.